Method and apparatus for spinal fixation

ABSTRACT

Disclosed is a fixation device for spinal fixation. The fixation device includes an elongated body comprising a bone anchor at a distal end. An axially moveable proximal anchor is carried by the proximal end of the fixation device. In one embodiment, the device is inserted through a first vertebra and the bone anchor is rotated into positioned within a second vertebra. The proximal anchor is distally advanced with respect to the bone anchor to provide compression across the first and second vertebra. In other embodiments, the device is used to secure stabilization devices across two or more vertebra.

PRIORITY INFORMATION

This application claims the priority benefit under 35 U.S.C. §119(e) ofProvisional Application 60/397,588 filed Jul. 19, 2002 and ProvisionalApplication 60/424,055 filed Nov. 5, 2002, the entire contents of theseProvisional Applications are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to medical devices and, more particularly,to methods and apparatus for spinal stabilization.

2. Description of the Related Art

The human spine is a flexible weight bearing column formed from aplurality of bones called vertebrae. There are thirty three vertebrae,which can be grouped into one of five regions (cervical, thoracic,lumbar, sacral, and coccygeal). Moving down the spine, there aregenerally seven cervical vertebra, twelve thoracic vertebra, five lumbarvertebra, five sacral vertebra, and four coccygeal vertebra. Thevertebra of the cervical, thoracic, and lumbar regions of the spine aretypically separate throughout the life of an individual. In contrast,the vertebra of the sacral and coccygeal regions in an adult are fusedto form two bones, the five sacral vertebra which into extend theformation of the sacrum and the four coccygeal vertebra which into thecoccyx.

In general, each vertebra contains an anterior, solid segment or bodyand a posterior segment or arch. The arch is generally formed of twopedicles and two laminae, supporting seven processes—four articular, twotransverse, and one spinous. There are exceptions to these generalcharacteristics of a vertebra. For example, the first cervical vertebra(atlas vertebra) has neither a body nor spinous process. Also, thesecond cervical vertebra (axis vertebra) has an odontoid process, whichis a strong, prominent process, shaped like a tooth, risingperpendicularly from the upper surface of the body of the axis vertebra.Further details regarding the construction of the spine may be found insuch common references as Gray's Anatomy, Crown Publishers, Inc., 1977,pp. 33-54, which is herein incorporated by reference.

The human vertebrae and associated connective elements are subjected toa variety of diseases and conditions which cause pain and disability.Among these diseases and conditions are spondylosis, spondylolisthesis,vertebral instability, spinal stenosis and degenerated, herniated, ordegenerated and herniated intervertebral discs. Additionally, thevertebrae and associated connective elements are subject to injuries,including fractures and torn ligaments and surgical manipulations,including laminectomies.

The pain and disability related to the diseases and conditions oftenresult from the displacement of all or part of a vertebra from theremainder of the vertebral column. Over the past two decades, a varietyof methods have been developed to restore the displaced vertebra totheir normal position and to fix them within the vertebral column. Suchmethods typically include various fixation systems that are used for thestabilization of fractures and/or fusions of various portions of thespine. These fixation systems may include a variety of longitudinalelements such as rods or plates which span two or more vertebra and areaffixed to the vertebra by various fixation elements such as wires,staples, and screws (often inserted through the pedicles of thevertebra). These systems may be affixed to either the posterior or theanterior side of the spine. In other applications, one or more bonescrews may be inserted through adjacent vertebrae to providestabilization.

Notwithstanding the variety of efforts in the prior art, there remains aneed for an orthopedic fixation device for spinal fixation with improvedlocking force, which resists migration and rotation, and which can beeasily and rapidly deployed within the spine.

SUMMARY OF THE INVENTION

There is provided in accordance with one aspect of the presentinvention, a method of providing compression across two vertebra. Themethod comprises advancing a fixation device having a distal portionwith a bone anchor and a proximal portion through a portion of a firstvertebra and positioning the bone anchor into a second vertebra. Aproximal anchor is axially advanced to provide compression across thetwo vertebra. In one embodiment, the bone anchor is rotated to securethe fixation device to the first vertebra. In other embodiments, thefixation device is advanced through the inferior facet of a superiorvertebra and into the base of the transverse process of the immediatelyinferior vertebra. In other embodiments, the fixation device is advancedthrough the inferior facet of a superior vertebra and into the base ofthe facet or pedicle of the immediately inferior vertebra. These methodsmay additionally comprise the step of uncoupling the first portion fromthe second portion, such as for device removal following fusion. Inaddition, the method may include repeating some of these steps toprovide bilateral symmetry.

There is provided in accordance with one aspect of the presentinvention, a method of providing compression across two vertebra. Themethod comprises advancing a fixation device having a distal portionwith a bone anchor and a proximal portion through a portion of a firstvertebra and positioning the bone anchor into a second vertebra, thefixation device may be advanced through an aperture on an implantablesupport structure such as a plate, a rod or a cage, and anchored into avertebral body to attach the support structure to the vertebral body.

In accordance with another embodiment of the present invention, a spinalfixation device comprises an elongate body, having a proximal end and adistal end; a distal anchor on the distal end; a retention structure onthe body, proximal to the distal anchor; and a proximal anchor, moveablycarried by the body. At least one complementary retention structure isprovided on the proximal anchor and is configured to permit proximalmovement of the body with respect to the proximal anchor but resistdistal movement of the body with respect the proximal anchor. A flangeis configured to receive the proximal anchor, The proximal anchor andthe flange having complementary surface structures to permit angularadjustment with respect to the longitudinal axis of the proximal anchorand the body and the longitudinal axis of the flange.

In accordance with another embodiment of the present invention, a methodof providing spinal fixation comprises the steps of advancing a fixationdevice that comprises a body having a first portion that forms a boneanchor and a second portion that forms a proximal end; through a portionof a first vertebra, advancing the bone anchor of the fixation deviceinto a second vertebra, advancing a proximal anchor distally along thefixation device; and distally advancing proximal anchor with respect tothe body to adjust compression across the first and second vertebrae.

In accordance with another embodiment of the present invention, a methodof providing spinal fixation comprises the steps of advancing a firstfixation device that comprises a body having a first portion that formsa distal bone anchor and a second portion that forms a proximal end intoa first vertebra, advancing a second fixation device that comprises abody having a first portion that forms a distal bone anchor and a secondportion that forms a proximal end into a second vertebra, coupling afirst portion of a fixation structure to the first fixation device,coupling a second portion of the fixation structure to the secondfixation device, securing the first fixation structure to the firstvertebra by advancing a first proximal anchor distally along the body ofthe first fixation device and proximally retracting the proximal anchorwith respect to the body; and securing the second fixation structure tothe second vertebra by advancing a second proximal anchor distally alongthe body of the second fixation device and proximally retracting thesecond proximal anchor with respect to the body.

Further features and advantages of the present invention will becomeapparent to those of skill in the art in view of the detaileddescription of preferred embodiments which follows, when consideredtogether with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a side elevational view of a portion of a vertebra having aexemplary embodiment of a fixation device implanted therein.

FIG. 2 is a side perspective view of an exemplary fixation devicesimilar to that of FIG. 1.

FIG. 3 is a side elevational view of the fixation device of FIG. 2.

FIG. 4 is a cross-sectional view taken through line 4-4 of FIG. 3.

FIG. 4A is an enlarged view of portion 4A of FIG. 4.

FIG. 4B is an enlarged view of portion 4B of FIG. 4 with the fixationdevice in a first position.

FIG. 4C is an enlarged view of portion 4C of FIG. 4 with the fixationdevice in a second position.

FIG. 5 is a cross-sectional view taken through line 5-5 of FIG. 3.

FIG. 6A is a side perspective view of another embodiment of a proximalanchor for the bone fixation device of FIG. 1.

FIG. 6B is a cross-sectional view of the proximal anchor of FIG. 6A.

FIG. 6C is a side perspective view of another embodiment of a proximalanchor for the bone fixation device of FIG. 1.

FIG. 6D is a cross-sectional view of the proximal anchor of FIG. 6C.

FIG. 6E is a cross-sectional view of another embodiment of a proximalanchor for the bone fixation device of FIG. 1.

FIG. 6F is a cross-sectional view of the proximal anchor of FIG. 6E.

FIG. 7 is a cross sectional view through an angularly adjustableproximal anchor plate.

FIG. 8 is a front perspective view of the proximal anchor plate of FIG.7.

FIG. 9 is a bottom perspective view of a modified embodiment of a bonefixation device.

FIG. 10 is an unassembled side perspective view of the bone fixationdevice of FIG. 9.

FIG. 11 is an unassembled side view of the bone fixation device of FIG.9.

FIG. 12 is a cross-sectional view of the flange and proximal anchor ofthe bone fixation device of FIG. 11.

FIG. 13 is an unassembled bottom perspective view of the bone fixationdevice of FIG. 9.

FIG. 14 is an unassembled side perspective view of another modifiedembodiment of a bone fixation device.

FIG. 15 is an unassembled side view of the bone fixation device of FIG.9.

FIG. 16 is a posterior view of a portion of the spinal column and afixation system including the fixation device of FIG. 1.

FIG. 17 is a posterior view of the spinal column and a modified fixationsystem that includes the fixation device of FIG. 1.

FIG. 18 is a posterior view of a portion of the lumbar spine with thefixation device of FIG. 9 used as a trans-facet screw.

FIG. 19 is a posterior view of a portion of the lumbar spine with thefixation device of FIG. 9 used as a trans-laminar screw.

FIG. 20 is a posterior view of a portion of the lumbar spine with thefixation device of FIG. 9 used as a facet-pedicle screw.

FIG. 21 is a side perspective view of another embodiment of a bonefixation device.

FIG. 22 is a front view of the bone fixation device of FIG. 20.

FIG. 23 is a cross-sectional view of the bone fixation device of FIG.20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the fixation devices of the present invention will be disclosedprimarily in the context of a spinal fixation procedure, the methods andstructures disclosed herein are intended for application in any of avariety medical applications, as will be apparent to those of skill inthe art in view of the disclosure herein. For example, the bone fixationdevice may be applicable to proximal fractures of the femur and a widevariety of fractures and osteotomies, the hand, such as interphalangealand metacarpophalangeal arthrodesis, transverse phalangeal andmetacarpal fracture fixation, spiral phalangeal and metacarpal fracturefixation, oblique phalangeal and metacarpal fracture fixation,intercondylar phalangeal and metacarpal fracture fixation, phalangealand metacarpal osteotomy fixation as well as others known in the art.See e.g., U.S. Pat. No. 6,511,481, which is hereby incorporated byreference herein. A wide variety of phalangeal and metatarsalosteotomies and fractures of the foot may also be stabilized using thebone fixation devices described herein. These include, among others,distal metaphyseal osteotomies such as those described by Austin andReverdin-Laird, base wedge osteotomies, oblique diaphyseal, digitalarthrodesis as well as a wide variety of others that will be known tothose of skill in the art. Fractures of the fibular and tibial malleoli,pilon fractures and other fractures of the bones of the leg may befixated and stabilized with these bone fixation devices with or withoutthe use of plates, both absorbable or non-absorbing types, and withalternate embodiments of the current invention. The fixation devices mayalso be used to attach tissue or structure to the bone, such as inligament reattachment and other soft tissue attachment procedures.Plates and washers, with or without tissue spikes for soft tissueattachment, and other implants may also be attached to bone, usingeither resorbable or nonresorbable fixation devices depending upon theimplant and procedure. The fixation devices may also be used to attachsutures to the bone, such as in any of a variety of tissue suspensionprocedures. The bone fixation device described herein may be used withor without plate(s) or washer(s), all of which can be either permanent,absorbable, or combinations.

Referring to FIG. 1, there as illustrated a side elevational view of anexemplary embodiment of a bone fixation device 12. In FIG. 1, a pair offixation devices 12 are positioned within adjacent vertebrae 10. As willbe explained in more detail below, the bone fixation device 12 may beused in a variety of techniques to stabilize the spine. For example, thebone fixation devices 12 may be used as pedicle or facet screws that maybe unilaterally or bilaterally symmetrically mounted on adjacent ornon-adjacent vertebrae and used in combination one or more linkage rodsor plates to facilitate fusion of one or more vertebrae. The bonefixation devices 12 disclosed herein may also be used as a fixationscrew to secure two adjacent vertebra to each other in a trans-laminar,trans-facet or facet-pedicle (e.g., the Boucher technique) applications.One of skill of the art will also recognize that the bone fixationdevices disclosed herein may be used for posterior stability afterlaminectomy, artificial disc replacement, repairing odontoid fracturesand other fractures of the spine, and other applications for providingtemporary or permanent stability in the spinal column.

Referring to FIGS. 2-4, the exemplary fixation device 12 will now bedescribed in detail. The fixation device 12 comprises a body 28 thatextends between a proximal end 30 and a distal end 32. The length,diameter and construction materials of the body 28 can be varied,depending upon the intended clinical application. In embodimentsoptimized for spinal fixation in an adult human population, the body 28will generally be within the range of from about 20-90 mm in length andwithin the range of from about 3.0-8.5 mm in maximum diameter. Thelength of the helical anchor, discussed below, may be about 8-80millimeters. Of course, it is understood that these dimensions areillustrative and that they may be varied as required for a particularpatient or procedure.

In one embodiment, the body 28 comprises titanium. However, as will bedescribed in more detail below, other metals or bioabsorbable ornonabsorbable polymeric materials may be utilized, depending upon thedimensions and desired structural integrity of the finished fixationdevice 12.

The distal end 32 of the body 28 is provided with a cancellous boneanchor or distal cortical bone anchor 34. Generally for spinal fixation,the distal bone anchor 34 is adapted to be rotationally inserted into aportion (e.g., the facet or pedicle) of a first vertebra. In theillustrated embodiment, the distal anchor 34 comprises a helical lockingstructure 72 for engaging cancellous and/or distal cortical bone. In theillustrated embodiment, the locking structure 72 comprises a flange thatis wrapped around an axial lumen. The flange extends through at leastone and generally from about two to about 50 or more full revolutionsdepending upon the axial length of the distal anchor and intendedapplication. The flange will generally complete from about 2 to about 20revolutions. The helical flange 72 is preferably provided with a pitchand an axial spacing to optimize the retention force within cancellousbone, to optimize compression.

The helical flange 72 of the illustrated embodiment has a generallytriangular cross-sectional shape (see FIG. 4). However, it should beappreciated that the helical flange 72 can have any of a variety ofcross sectional shapes, such as rectangular, oval or other as deemeddesirable for a particular application through routine experimentationin view of the disclosure herein. The outer edge of the helical flange72 defines an outer boundary. The ratio of the diameter of the outerboundary to the diameter of the central lumen can be optimized withrespect to the desired retention force within the cancellous bone andgiving due consideration to the structural integrity and strength of thedistal anchor 34. Another aspect of the distal anchor 34 that can beoptimized is the shape of the outer boundary and the central core, whichin the illustrated embodiment are generally cylindrical.

The distal end 32 and/or the outer edges of the helical flange 72 may beatraumatic (e.g., blunt or soft). This inhibits the tendency of thefixation device 12 to migrate anatomically distally and potentially outof the vertebrae after implantation. Distal migration is also inhibitedby the dimensions and presence of a proximal anchor 50, which will bedescribed below. In the spinal column, distal migration is particularlydisadvantageous because the distal anchor may harm the tissue, nerves,blood vessels and spinal cord which lie within and/or surround thespine.

A variety of other arrangements for the distal anchor 32 can also beused. For example, the various distal anchors described in co-pendingU.S. patent application Ser. No. 10/012,687, filed Nov. 13, 2001 can beincorporated into the fixation device 12 described herein. The entirecontents of this application is hereby expressly incorporated byreference. In particular, the distal anchor may comprise a singlehelical thread surrounding a central core, much as in a conventionalscrew, which has been cannulated to facilitate placement over a wire.Alternatively, a double helical thread may be utilized, with the distalend of the first thread rotationally offset from the distal end of thesecond thread. The use of a double helical thread can enable a greateraxial travel for a given degree of rotation and greater retention forcethan a corresponding single helical thread. Specific distal anchordesigns can be optimized for the intended use, taking into accountdesired performance characteristics, the integrity of the distal bone,and whether the distal anchor is intended to engage exclusivelycancellous bone or will also engage cortical bone.

With particular reference to FIGS. 3, 4, and 4A, the body 28 comprises afirst portion 36 and a second portion 38 that are coupled together at ajunction 40. In the illustrated embodiment, the first portion 36 carriesthe distal anchor 34 while the second portion 38 forms the proximal end30 of the body 28. As will be explained in more detail below, in certainembodiments, the second portion 38 may be used to pull the body 28 andtherefore will sometimes be referred to as a “pull-pin”. The first andsecond portions 36, 38 are preferably detachably coupled to each otherat the junction 40. In the illustrated embodiment, the first and secondportions 36, 38 are detachably coupled to each other via interlockingthreads. Specifically, as best seen in FIG. 4A, the body 28 includes aninner surface 41, which defines a central lumen 42 that preferablyextends from the proximal end 30 to the distal end 32 throughout thebody 28. At the proximal end of the first portion 36, the inner surface41 includes a first threaded portion 44. The first threaded portion 44is configured to mate with a second threaded portion 46, which islocated on the outer surface 45 of the second portion 38. Theinterlocking annular threads of the first and second threaded portions44, 46 allow the first and second portions 36, 38 to be detachablycoupled to each other. In one modified embodiment, the orientation ofthe first and second threaded portions 44, 46 can be reversed. That is,the first threaded portion 44 can be located on the outer surface of thefirst portion 36 and the second threaded portion 46 can be located onthe inner surface 41 at the distal end of the second portion 38. Any ofa variety of other releasable complementary engagement structures mayalso be used, to allow removal of second portion 38 followingimplantation, as is discussed below.

In a modified arrangement, the second portion 38 can comprise any of avariety of tensioning elements for permitting proximal tension to beplaced on the distal anchor 34 while the proximal anchor is advanceddistally to compress the fracture. For example, any of a variety oftubes or wires can be removably attached to the first portion 36 andextend proximally to the proximal handpiece. In one such arrangement,the first portion 36 can include a releasable connector in the form of alatching element, such as an eye or hook. The second portion 38 caninclude a complementary releasable connector (e.g., a complementaryhook) for engaging the first portion 36. In this manner, the secondportion 38 can be detachably coupled to the first portion 36 suchproximal traction can be applied to the first portion 36 through thesecond portion as will be explained below. Alternatively, the secondportion 48 may be provided with an eye or hook, or transverse bar,around which or through which a suture or wire may be advanced, bothends of which are retained at the proximal end of the device. Followingproximal tension on the tensioning element during the compression step,one end of the suture or wire is released, and the other end may bepulled free of the device. Alternate releasable proximal tensioningstructures may be devised by those of skill in the art in view of thedisclosure herein. It should also be appreciated that the body may befrom a single piece as described in U.S. Pat. No. 6,511,481, which hasbeen incorporated by reference herein.

As shown in FIG. 4, the body 28 is cannulated to accommodateinstallation over a placement wire as is understood in the art. Thecross section of the illustrated central cannulation is circular but inother embodiments may be non circular, e.g., hexagonal, to accommodate acorresponding male tool for installation or removal of the secondportion 38 of the body 28 as explained above. In other embodiments, thebody 28 may partially or wholly solid.

With continued reference to FIGS. 2-4, the proximal end 30 of the body28 may be provided with a rotational coupling 70, for allowing thesecond portion 38 of the body 28 to be rotationally coupled to arotation device. The proximal end 30 of the body 28 may be desirablyrotated to accomplish one or two discrete functions. In one application,the proximal end 30 is rotated to remove the second portion 38 of thebody 28 following tensioning of the device to anchor an attachment tothe bone. Rotation of the rotational coupling 70 may also be utilized torotationally drive the distal anchor into the bone. Any of a variety ofrotation devices may be utilized, such as electric drills or hand tools,which allow the clinician to manually rotate the proximal end 30 of thebody. Thus, the rotational coupling 70 may have any of a variety ofcross sectional configurations, such as one or more flats or splines.

In one embodiment, the rotational coupling 70 comprises a proximalprojection of the body 28 having an axial recess with a polygonal crosssection, such as a hexagonal cross section. The rotational coupling 70is illustrated as a female component, machined or milled or attached tothe proximal end 30 of the body 28. However, the rotational coupling mayalso be in the form of a male element, such as a hexagonal or othernoncircular cross sectioned projection.

The proximal end 30 of the fixation device is provided with a proximalanchor 50. Proximal anchor 50 is axially distally moveable along thebody 28, to permit compression of between the distal and proximal ends32, 30 of the fixation device 12. As will be explained below,complimentary locking structures such as threads or ratchet likestructures between the proximal anchor 50 and the body 28 resistproximal movement of the anchor 50 with respect to the body 28 undernormal use conditions. The proximal anchor 50 preferably can be axiallyadvanced along the body 28 with and/or without rotation as will beapparent from the disclosure herein.

Referring to FIG. 4, the proximal anchor 50 comprises a housing 52 suchas a tubular body, for coaxial movement along the body 28. As will beexplained in more detail below, in certain embodiments, the housing 50may have diameter sized to fit through an opening formed in fixation baror plate.

In a final position, the distal end of the housing 52 preferably extendsdistally past the junction 40 between the first portion 36 and thesecond portion 38. The housing 52 is provided with one or more surfacestructures 54 such as a radially inwardly projecting flange 56 (seeFIGS. 4B and 4C), for cooperating with complementary surface structures58 on the first portion 36 of the body 28. In the illustratedembodiment, the complimentary surface structures 58 comprise a series ofannular ridges or grooves 60. The surface structures 54 andcomplementary surface structures 58 permit distal axial travel of theproximal anchor 50 with respect to the body 28, but resist proximaltravel of the proximal anchor 50 with respect to the body 28.

For example, as best seen in FIG. 4B, the proximal end of the flange 56is biased towards the longitudinal axis of the body 28. As such, whenthe proximal anchor 50 is urged proximally with respect to the body 28,the flange 56 engages the grooves or ridges 60 of the complementarysurface structures 58. This prevents proximal movement of the proximalanchor 50 with respect to the body 28. In contrast, as best seen in FIG.4C, when the proximal anchor 50 is moved distally with respect to thebody 28, the flange 56 can bend outwardly away from the body 28 and theridges 60 so as to allow the proximal anchor 50 to move distally. Ofcourse, those of skill in the art will recognize that there are avariety of other complementary surface structures, which permit one wayratchet like movement. For example, a plurality of annular rings orhelical threads, ramped ratchet structures and the like for cooperatingwith an opposing ramped structure or pawl can also be used. In oneembodiment, opposing screw threads are dimensioned to function as aratchet.

Retention structures 58 are spaced axially apart along the body 28,between a proximal limit 62 and a distal limit 64. The axial distancebetween proximal limit 62 and distal limit 64 is related to the desiredaxial working range of the proximal anchor 50, and thus the range offunctional sizes of the fixation device 12. Thus, the fixation device 12of the exemplary embodiment can provide compression between the distalanchor 34 and the proximal anchor 50 vertebrae throughout a range ofmotion following the placement of the distal anchor in a vertebra. Thatis, the distal anchor may be positioned within the cancellous and/ordistal cortical bone of a vertebra, and the proximal anchor may bedistally advanced with respect to the distal anchor throughout a rangeto provide compression without needing to relocate the distal anchor andwithout needing to initially locate the distal anchor in a preciseposition with respect to the proximal side of the bone or anothervertebra. Providing a working range throughout which tensioning of theproximal anchor is independent from setting the distal anchor allows asingle device to be useful for a wide variety of spinal fixationprocedures, as well as eliminates the need for accurate devicemeasurement. In addition, this arrangement allows the clinician toadjust the compression force during the procedure without adjusting theposition of the distal anchor. In this manner, the clinician may focuson positioning the distal anchor sufficiently within the vertebra toavoid or reduce the potential for distal migration out of the vertebra,which may damage the particularly delicate tissue, blood vessels, nervesand/or spinal cord surrounding or within the spinal column.

In many applications, the working range is at least about 10% of theoverall length of the device, and may be as much as 20% or 50% or moreof the overall device length. In the context of a spinal application,working ranges of up to about 10 mm or more may be provided, sinceestimates within that range can normally be readily accomplished withinthe clinical setting. The embodiments disclosed herein can be scaled tohave a greater or a lesser working range, as will be apparent to thoseof skill in the art in view of the disclosure herein.

With reference back to FIGS. 2-4, the proximal anchor 50 includes aflange 66 that, as will be explained below, may be configured to sitagainst the outer surface of a vertebra and/or a fixation rod or plate.The flange 66 is preferably an annular flange, to optimize the footprintor contact surface area between the flange 66 and the bone or fixationrod or plate. Circular or polygonal shaped flanges for use in spinalfixation will generally have a diameter of at least about 3 mm greaterthan the adjacent body 28 and often within the range of from about 2 mmto about 30 mm or more greater than the adjacent body 28.

With particular reference to FIGS. 2 and 5, the fixation device mayinclude an antirotation lock between the first portion 36 of the body 28and the proximal collar 50. In the illustrated embodiment, the firstportion 36 includes a pair of flat sides 80, which interact withcorresponding flat structures 82 in the proximal collar 50. One or threeor more axially extending flats may also be used. As such, rotation ofthe proximal collar 50 is transmitted to the first portion 36 and distalanchor 34 of the body 28. Of course, those of skill in the art willrecognize various other types of splines or other interfit structurescan be used to prevent relative rotation of the proximal anchor and thefirst portion 36 of the body 28.

To rotate the proximal collar, the flange 66 is preferably provided witha gripping structure to permit an insertion tool to rotate the flange66. Any of a variety of gripping structures may be provided, such as oneor more slots, flats, bores or the like. In one embodiment, the flange44 is provided with a polygonal, and, in particular, a pentagonal orhexagonal recess 84 (see FIG. 4).

In a modified embodiment, the housing 52 of the proximal anchor 50 caninclude one or more one or more barbs that extend radially outwardlyfrom the tubular housing 52. Such barbs provide for self tighteningafter the device has been implanted in the patient as described in aco-pending U.S. patent application Ser. No. 10/012,687, filed Nov. 13,2001, which was incorporated by reference above. The barbs may beradially symmetrically distributed about the longitudinal axis of thehousing 52. Each barb is provided with a transverse engagement surface,for anchoring the proximal anchor 50 in the bone. The transverseengagement surface may lie on a plane which is transverse to thelongitudinal axis of the housing 50 or may be inclined with respect tothe longitudinal axis of the tubular 50. In either arrangement, thetransverse engagement surface 43 generally faces the contacting surface68 of the flange 44. As such, the transverse engagement surface inhibitsproximal movement of the proximal anchor with respect to the bone.

FIGS. 6A and 6B illustrate another embodiment of a proximal anchor 100.This embodiment also includes a tubular housing 102 and a flange 104that may be configured as describe above with respect to FIGS. 2-4. Thetubular housing 102 may include an anti-rotational lock, which, in theillustrated embodiment, is in the form of one or more sides 106 thatinteract with corresponding flat structures formed in the body 28 asdescribed above.

In this embodiment, the surfaces structures comprises one or more teethor grooves 112, which are configured to engage the complementarysurfaces structures on the body 28 (see FIG. 2). One or more slots oropenings 110 are formed in the tubular housing 102 to form one or morebridges 112, which carry the teeth 102. The anchor proximal anchor 100may be pushed towards the distal end of the body and the teeth 102 canslide along the and over the complementary surface structures 58 on thebody 28. In the illustrated embodiment, the bridge 113 may flex slightlyaway from the body 28 to allow such movement. The number and shape ofthe openings 110 and bridges 112 may be varied depending of the desiredflexing of the bridges 112 when the proximal anchor 110 is moveddistally over the body and the desired retention force of the distalanchor when appropriately tensioned. In one embodiment, the teeth on theproximal anchor 100 and the grooves on the body 28 may be configuredsuch that the proximal anchor 100 can be rotated or threaded onto thepin in the distal direct and/or so that that the proximal anchor can beremoved by rotation. The illustrated embodiment also advantageouslyincludes visual indicia 114 (e.g., marks, grooves, ridges etc.) on thetubular housing 102 for indicating the depth of the proximal housing 100within the bone.

FIGS. 6C and 6D illustrate another embodiment of a proximal anchor 150.In this embodiment, the proximal anchor 150 comprises a housing 152 suchas a tubular body, for coaxial movement along the body 28. The proximalanchor 150 also includes a flange 154 that is configured that to setagainst the outer surface of, for example, a bone or fixation bar orrod. In the illustrated embodiment, the flange 154 defines a contactingsurface 156, which preferably forms an obtuse angle with respect to theexterior of the housing 152. However, in modified embodiments, thecontacting surface 154 may be perpendicular or form an acute angle withrespect to the housing 152.

Referring to FIG. 6D, in the illustrated embodiment, the complementaryretention structures 54 comprise one or more inwardly projecting teethor flanges 158, for cooperating with the complementary rententionstructures 58 on the body 28. The complementary retention structures 58of the body preferably comprise a plurality of annular ridges or groovesa first surface and a second surface. The first surface generally facesthe proximal direction and is preferably inclined with respect to thelongitudinal axis of the body 28. In contrast, the second surfacegenerally faces the distal direction and lies generally perpendicular tothe longitudinal axis of the body 28.

The proximal anchor 150 preferably includes one or more of axial slots160. The axial slots 160 cooperate to form lever arm(s) on which theteeth or projections 158 are positioned. Thus, as the anchor 150 ispushed towards the distal end of the body 28, the teeth 158 can slidealong the first surface and ride over the retention structures 58 of thebody 28 as the teeth 158 are flexed away from the body 28.

After appropriate tensioning of the proximal anchor 150, the bone maypush on the angled portion contacting surface 156 of the proximal anchor150. This force is transmitted to the teeth 158 through the lever arms.As such, the teeth 158 are prevented from flexing away from the body 28,which keeps the teeth 158 engaged with the retention structures 58 ofthe body 28. By increasing the tensioning force, proximal movement ofthe proximal anchor 150 with respect to the body 28 is resisted.

The axial length and width of the slots 160 may be varied, dependingupon the desired flexing of the lever arms when the proximal anchor 150is moved distally over the body 28 and the desired retention force ofthe distal anchor when appropriately tensioned. For a relatively rigidmaterial such as titanium, axial lengths and widths of the slots 160 areapproximately 0.5 mm for a proximal anchor having a length ofapproximately 4 mm, an inner diameter of approximately 3 mm. As such, inthe illustrated embodiment, the slots 160 extend through the flange 154and at least partially into the housing 152.

In this embodiment, the proximal anchor 150 includes four teeth orflanges 158, which are positioned near the proximal end of the anchor150. In modified embodiments, the proximal anchor 150 may include moreor lest teeth and/or the teeth may be positioned more distally orproximally on the anchor 150. It should also be appreciated that theseretention structures may be configured such that the proximal anchor 150may be proximally and/or distally advanced with rotation by providingfor a screw like configuration between the retention structures.

Another embodiment of a proximal anchor 180 is illustrated in FIGS. 6Eand 6F. As with the previous embodiment, the proximal anchor 180 mayinclude a tubular housing 152 and a flange 154 with a bone contactingsurface 156. In this embodiment, the complementary structure of theproximal anchor 180 comprises an annular ring 182, which is positionedwithin an annular recess 184 that is preferably positioned at the distalend of the tubular housing 152. The annular recess 184 includes aproximal portion 186 and a distal portion 188.

The proximal portion 186 is sized and dimensioned such that as theproximal anchor 180 is advanced distally over the body 28 the annularring 182 can ride over the complementary retention structures 58 of thebody 28. That is, the proximal portion 182 provides a space for theannular ring 182 can move radially away from the body 28 as the proximalanchor 180 is advanced distally. Preferably, the annular ring 182 ismade from a material that provides sufficient strength and elasticitysuch as, for example, stainless steel or titanium. The annular ring 182is preferably split such that it can be positioned over the body 405. Inthe illustrated embodiment, the annular ring 182 includes a plurality ofteeth 192 although in modified embodiments the annular ring 182 may beformed without the teeth.

The distal portion 188 of the recess 184 is sized and dimensioned suchthat after the proximal anchor 180 is appropriately tensioned theannular ring 192 becomes wedged between the body 28 and an angledengagement surface of the distal portion 188. In this manner, proximalmovement of the proximal anchor 180 with respect to the body isprevented. Although not illustrated, it should be appreciated that inmodified embodiments, the ring 192 can be formed without a gap. Otherembodiments and further details of the proximal anchor described abovecan be found in U.S. patent application Ser. No. 09/990,587, filed Nov.19, 2001, which is hereby incorporated by reference herein.

With reference back to FIGS. 2-4, in the illustrated embodiment, thecontacting surface 68 of the flange 44 is tapered and generally facesthe outer surface of the vertebra, fixation rod, and/or plate. In otherembodiments, the bone contacting surface 69 can reside in orapproximately on a plane, which is perpendicular with respect to thelongitudinal axis of the body 28. In other embodiments, other angularrelationships between the bone contacting surface 68 of the flange 66and the longitudinal axis of the body 28 and housing 52 may be utilized,depending upon the anticipated entrance angle of the body 28 andassociated entrance point surface of the vertebra.

The clinician may be provided an array of proximal anchors 50 of varyingangular relationships between the contacting surface 68 and thelongitudinal axis of the body 28 and housing 52 (e.g., 90°, 100°, 110°,120°, and 130°). A single body 28 can be associated with the array suchas in a single sterile package. The clinician upon identifying theentrance angle of the body 28 and the associated entrance point surfaceorientation of the facet joint of the spine can choose the anchor 50from the array with the best fit angular relationship, for use with thebody 28.

In accordance with a modified arrangement, illustrated in FIGS. 7 and 8,the proximal anchor 50 may be used with a washer 66′ that is angularlyadjustable with respect to the longitudinal axis of the body 28. Morespecifically, in this embodiment, the proximal anchor 50 and the washer66′ include corresponding semi-spherical or radiused surfaces 45 a and45 b. The surface 45 b surrounds an aperture 49 in the washer 66. Thisarrangement allows the proximal anchor 50 to extend through and pivotwith respect to the washer 66′. As such, the angular relationshipbetween the bone contacting surface 68′ of the washer 66′ and thelongitudinal axis of the body 28 can vary in response to the entranceangle.

FIGS. 9-13 illustrate another embodiment of a bone fixation device 200with an angularly adjustable proximal anchor 202. In this embodiment,similar reference numbers are used to identify components that aresimilar components described above.

The bone fixation device 200 comprises a body 28 that extending betweena proximal end 30 and a distal end 32. The distal end 32 of the body isprovide with a bone anchor 34 as described above. The illustrated body28 is cannulated; however, it should be appreciated that in modifiedembodiments the body 28 can be solid. The proximal end of the anchor isprovided with a hexagonal recess, which can be used in combination witha rotational tool to rotate the body 28. Of course, modified embodimentsmay use a variety of different male or female anti-rotational couplings.

The illustrated fixation device includes an annular flange 202 andproximal anchor 204. As with the proximal anchor described above, theproximal anchor 204 defines a housing 206 that is axially distallymoveable along the body 28. Complimentary locking structures 54, 58 onthe housing 206 and the body 28 such as threads or ratchet likestructures resist proximal movement of the anchor 204 with respect tothe body 28 under normal use conditions. In some embodiments, thecomplimentary locking structures 54, 48 may permit the anchor 204 to beaxially advanced along the body 28 by rotation. In other embodiments,the complimentary locking structures 54, 58 may permit the anchor 204 tobe axially advanced along the body 24 without rotation. The illustratedproximal anchor 204 also includes a gap 205 such that the illustratedanchor 204 forms a split ring collar. In modified embodiments, theproximal anchor 204 can be formed without the gap 205.

The proximal anchor 204 preferably includes a smooth and more preferablyrounded or spherical outer surface portion 208, which is configured tofit within a corresponding smooth and preferably rounded recessedportion 210 in the flange 202. As such, as shown in FIG. 12, when theproximal anchor 204 is positioned in the flange 202, the flange 202resists distal movement of the proximal anchor 204 while permitting atleast limited rotation of between the proximal anchor 204 and the flange202. As such, the illustrate arrangement allows for angular movement ofthe flange 202 with respect to the anchor 204 to accommodate variableanatomical angles of the bone surface. As will be explained in moredetail below, this embodiment is particularly advantageous fortrans-laminar, trans-facet and facet-pedicle applications. In suchapplications, the flange 202 may seat directly against the outer surfaceof a vertebra. Because the outer surface of the vertebra is typicallynon-planar and/or the angle of insertion is not perpendicular to theouter surface of the vertebra, a fixed flange may contact only a portionof the outer surface of the vertebra. This may cause the vertebra tocrack due to high stress concentrations. In contrast, the angularlyadjustable flange 202 can rotate with respect to the body and therebythe bone contacting surface may be positioned more closely to the outersurface. More bone contacting surface is thereby utilized and the stressis spread out over a larger area. In addition, the flange 202, which hasa larger diameter than the proximal anchor 50, effectively increases theshaft to head diameter of the fixation device, thereby increasing thesize of the loading surface and reducing stress concentrations.

In the illustrated embodiment, the flange 202 includes a plurality ofbone engagement features 212, which in the illustrated embodimentcomprises a one or more spikes 212 positioned on a contacting surface216 of the flange 202. The spikes 212 provide additional grippingsupport especially when the flange 202 is positioned against, forexample, uneven bone surfaces and/or soft tissue. However, it should beappreciated that in modified embodiments the flange 202 may be formedwithout the bone engagement features 212. Other structures for the boneengagement feature 212 may also be used, such as, for example, ridges,serrations etc. The illustrated embodiment also includes a tapered uppersurface 214 that in certain embodiments may be flat.

FIGS. 14 and 15 illustrate a modified embodiment of the angularityadjustable fixation device 200. In this embodiment, the proximal anchor204′ includes an upper portion 211 and a lower portion 213. The upperportion 211 is configured as described above with respect to thehousing. The lower portion in the illustrated embodiment is generallytubular and a generally smaller diameter than the upper portion. Thelower portion includes complementary retention structures 54 andgenerally provides the fixation device with a greater range ofadjustable compression and additional retention structures as comparedto the previous embodiment.

In one embodiment of use, a patient with a spinal instability isidentified. Depending upon the spinal fixation technique, the distalends 32 of one or more bone fixation devices described herein areadvanced into the anterior vertebral body or other suitable portion ofone or more vertebrae. As will be explained in more detail below, thefixation device is typically used to couple one vertebra that isunstable, separated or displaced to another vertebra, which is notunstable, separated or displaced. However, it should be appreciated thatthis method may also be applied to three or more vertebrae. In addition,the S-1 portion of the sacrum may be used to stabilize the L5 vertebrae.

For example, the fixation devices may be inserted into the vertebraewith bilateral symmetry such that such two vertebrae are coupledtogether with two or more fixation devices on a left side of the spinebeing connected using one or more rods and/or plates to two or morefixation devices on a right side of the spine. In certain of theseembodiments, the distal anchor of these fixation devices may be insertedthrough the pedicle and/or the facet of the vertebrae. In otherembodiments, the fixation devices will be utilized to secure adjacentvertebral bodies in combination with another fusion procedure orimplant, such as the implantation of a spinal cage, plate or otherdevice for fusing adjacent vertebral bodies. Thus, the fixation devicesmay operate in conjunction with a cage or other implant to provide threepoint stability across a disc space, to assist in resisting mobilitybetween two vertebral bodies. In other embodiments, the fixation devicemay simply be advanced through a portion of a first vertebra and into asecond, preferably adjacent, vertebra. In certain of these embodiments,the fixation device may extend through the facet of the first vertebraand the distal anchor may be inserted through the facet or pedicle ofthe second vertebra.

The proximal anchor may be carried by the fixation device prior toadvancing the body into the vertebrae, or may be attached followingplacement of the body within the vertebrae. In one embodiment,stabilization implants (e.g., a fixation plate and/or rod) may be placedover or coupled to the body or the proximal anchor before the proximalanchor is placed on the body.

Once the anchor is in the desired location, proximal traction is appliedto the proximal end 30 of body 28, such as by conventional hemostats,pliers or a calibrated loading device, while distal force is applied tothe proximal anchor. In this manner, the proximal anchor is advanceddistally with respect to the body until the proximal anchor fits snuglyagainst the outer surface of the vertebra or a fixation plate/rod.Appropriate tensioning of the fixation device is accomplished by tactilefeedback or through the use of a calibration device for applying apredetermined load on the implantation device. As explained above, oneadvantage of the structure of the illustrated embodiments is the abilityto adjust compression independently of the setting of the distal anchor34 within the vertebra.

Following appropriate tensioning of the proximal anchor, the secondportion 38 of the body 28 is preferably detached from the first portion36 and removed. In the illustrated embodiment, this involves rotatingthe second portion 38 with respect to the first portion via the coupling70. In other embodiment, this may involve cutting the proximal end ofthe body 28. For example, the proximal end of the body may be separatedby cauterizing. Cauterizing may fuse the proximal anchor 50 to the body32 thereby adding to the retention force between the proximal anchor 50and the body 28. Such fusion between the proximal anchor and the bodymay be particularly advantageous if the pin and the proximal anchor aremade from a bioabsorbable and/or biodegradable material. In this manner,as the material of the proximal anchor and/or the pin is absorbed ordegrades, the fusion caused by the cauterizing continues to provideretention force between the proximal anchor and the body.

Following or before removal of the second portion 38 of each body 28,additional fixations devices may be implanted and/or additionalstabilization implants (e.g., rods, plates, etc.) may be coupled to thebody. The access site may be closed and dressed in accordance withconventional wound closure techniques.

In a modified arrangement, the second portion 38 may form part of thedriving device, which is used to rotate the proximal anchor 50 and thuscancellous bone anchor 34 into the vertebrae. The second portion 38 isused to apply proximal traction. After appropriate tensioning, thesecond portion 38 can be de-coupled from the first portion 36 andremoved with the driving device.

In the foregoing variation, the second portion 38 may be connected to arotatable control such as a thumb wheel on the deployment device. Acontainer may be opened at the clinical site exposing the proximal endof the implant, such that the distal end of the second portion 38 may beremovably coupled thereto. Proximal retraction of the hand tool willpull the implant out of its packaging. The implant may then bepositioned within the aperture in the bone, rotated to set the distalanchor, and the hand piece may be manipulated to place proximal tractionon the second portion 38 while simultaneously distally advancing theproximal anchor. Following appropriate tensioning, the second portion 38may be disengaged from the implant, and removed from the patient. In theexample of a threaded engagement, the second portion 38 may bedisengaged from the implant by rotating a thumb wheel or otherrotational control on the hand piece. In an alternate embodiment, suchas where the second portion 38 comprises a pull wire, followingappropriate tensioning across the fracture, a first end of the pull wireis released such that the pull wire may be removed from the implant byproximal retraction of the second end which may be attached to the handpiece.

Preferably, the clinician will have access to an array of fixationdevices 12, having, for example, different diameters, axial lengths and,if applicable, angular relationships. These may be packaged one or moreper package in sterile or non-sterile envelopes or peelable pouches, orin dispensing cartridges which may each hold a plurality of devices 12.The clinician will assess the dimensions and load requirements, andselect a fixation device from the array, which meets the desiredspecifications.

As mentioned above, the fixation device 12 of may be used with a varietyspinal cages, plates or other devices for fusing adjacent vertebralbodies. For example, FIG. 16 illustrates a pair of fixation devicesscrews 12A, 12B according to the exemplary embodiments being used with apair of fixation bars 300, 302 for spinal fixation. In this embodiment,the fixation devices 12A, 12B and the fixation bars 300, 302 areillustrated as fixing the L3 and L4 vertebrae relative to each other;however, theses components can be used to fix other adjacent ornon-adjacent vertebrae in the lumbar region, as well as thethoracolumbar junction, or elsewhere on the spine as long as an axialpath between two vertebra to compress the two vertebrae.

As shown in FIGS. 16 and 17, a laminectomy has been performed on the L3and L4 vertebrae. Thus, the spinous process and the underlying lamina oneach side of the sagittal plane have been removed, leaving only theoutlying portion of the lamina transverse of the sagittal plane on boththe L3 and L4 vertebrae. In one embodiment, the first fixation device12A is inserted through the lamina of the L3 vertebra in the region ofthe facet joint on the left side of the sagittal plane. The firstfixation device 12A will extend in an anterior direction through thefacet joint and angles laterally outwardly into the left base of thetransverse process of the inferior vertebra L4. A second fixation device12B extends in an anterior direction through the lamina on the opposite(right) side of the sagittal plane. The second fixation device 12Bextends through the facet joint on the right side of the sagittal planeand angles laterally outwardly into the right base of the transverseprocess of the L4 vertebra. Thus, the fixation devices 12A, 12B divergein the anterior direction, and are also angled slightly in the inferiordirection.

Each of the fixation devices 12A, 12B may be fitted within a fixationbar 300, 302. It should be appreciated that the fixation bar 300, 302 ofFIG. 15 is merely exemplary and the fixation device may be used withother types and styles of fixation bars.

In the illustrated embodiment, the fixation bars 300 and 302 aregenerally mirror images of each other. The exemplary fixation bars 300,302 includes an inferior portion 304 having a plurality of cylindricalbores 306. Each of the bores 306 are generally oriented along parallelaxes and spaced in an inferior-superior direction along the inferior barportion 304. The fixation devices 12A, 12B extend through one of thebores 306. By choosing the appropriate bore 306 for the fixation bar300, 304, the relative length of the bar 300, 302 can be varied toprovide adjustability for different sized vertebra. Each bar 300, 302has a finger 308 that extends in a superior, and slightly lateral,direction from the inferior portion 306. The finger 308 extends in asuperior direction across the cephalad side of the lateral process of L3and curves in a superior and anterior direction over the superior aspectof the lateral pedicle of L3. The finger 308 then extends in an inferiordirection and slightly laterally inwardly before terminating in ananterior end 316 short of the spinal cavity 50. The superior portion ofthe finger 308 thus forms a hook that extends over and around the L3pedicle to secure the bar from movement in an inferior direction as wellas to prevent rotational movement about the longitudinal axis of thebar.

The body 28 of the fixation device can be inserted through the bore 306.The housing 52 of the proximal anchor 50 is also dimensioned such thatit has a diameter that is slightly less than the diameter of the bores42 so as to allow rotational and reciprocal movement of the fixationdevice 12A, 12B in the bore 306, but not to allow the fixation device12A, 12B toggle relative to its longitudinal axis. The flange 66 of theproximal anchor 50 has a diameter that is larger than the bore 42. Thus,the combination of the finger 44 wrapped around the superior portion ofthe lateral process 46 and the coaction of the fixation device 12Aholding inferior portion 304 in place will prevent the toggling of thefixation device 12A, 12B relative to the lamina on the superiorvertebra.

The inferior portion 304 of the bar 300, 302 may also carry a pluralityof lateral weakened zones 318 in the form of lateral notches on bothsurfaces of the inferior portion 304 between each of the bores 306. Withthe manipulation of the proper tool, one or more sections containingbores 306 can be broken away from the stabilization bar to adjust thelength of the inferior portion 304, so that unnecessary portions of theinferior portion can be removed. In FIG. 16, the left stabilization bar300 is shown with the lower two segments of the inferior portionremoved. In addition, the second portion 38 of the body 28 (see FIG. 4)are also illustrated as being removed after the stabilization bars 300and 302.

Proximal retraction of the body 28 with respect to the proximal anchor50 will compress the inferior portion 304 against the vertebra and willhold the stabilization bars 300, 302 rigidly and prevent toggling of thescrews. One advantage of the illustrated embodiment is that compressionof the inferior portion 304 against the vertebra may be adjustedindependently of the setting of the distal anchor in the spine.

FIG. 17 illustrates a modified embodiment of a spinal fixation system.In this embodiment, four fixation devices 12A, 12B, 12C, 12D, arepositioned in the facets of adjacent vertebra on both the left and rightside of the vertebra column. A first set of the fixation devices 12A,12B are used to secure opposing ends of a first fixation plate 400 tothe facets of adjacent vertebrae and a second set of fixation devices12C, 12D are be used to secure opposing ends of a second fixation plate400′ to the opposing facets on the adjacent vertebra. The fixationplates 400, 400′ may include a series of overlapping bores 401 throughwhich the body of the fixation device 12A, 12B may extend. The proximalanchor 50 may then be inserted over the body (not shown) and proximalretraction may be used to secure the fixation plate 400 against thevertebra.

The fixation hardware may also include cross-links 402, which spanacross the midline between corresponding fixation devices 12A, 12B, 12C,12D on opposite sides of the spine. The cross-links 402 also includesbores through which the body and the tubular portion of the housing 50extends. In modified embodiments, the fixation hardware may not includethe cross-links 402.

Although not illustrated, it should be appreciated that the fixationdevices described herein may be used as pedicle screws to secure afixation rod or plate that extends between two or more vertebrae. Suchapplications may be used unilaterally or with bilateral symmetry.

In the embodiments of FIGS. 16 and 17, the use of the fixation device 12advantageously allows the compression of the plates or fixation barsagainst the vertebrae to be adjusted independently of the setting of thedistal anchor 34. That is, the proximal anchor 50 is advanced distallywith respect to the body 28 until the proper compression load is appliedacross the fixation bars/plates and the vertebrae.

In a modified embodiment, the proximal anchor can be coupled to or forma part of the plate or fixation bar. Such an arrangement provides forself tightening after the device has been implanted into the patient.

As shown in FIG. 18, the fixation devices 12A, 12B may be used toprovide stability without additional hardware. In this example, thefixation device 12A, 12B is used as a trans-facet screw. That is, thefixation device extends through a facet of a first vertebra and into thefacet of a second, typically inferior, vertebrae. As in the illustratedembodiment, this procedure is typically (but not necessarily) preformedwith bilateral symmetry. Thus, even in the absence of a stabilizing bartying pedicle screws to adjacent vertebrae or to the sacrum, and in theabsence of translaminar screws that can extend through the spinousprocess, the fixation devices 12A, 12B can be used to stabilize twovertebrae, such as L3 and L4 to each other pending the healing of afusion. In one embodiment, the body 28 of fixation devices 12A, 12B hasa length of approximately 10 mm-30 mm and the diameter of the body isapproximately 3 mm to 5.5 mm.

FIG. 19 illustrates a modified arrangement for spinal fixation in whichthe fixation devices 12A′, 12B′ are used as trans-laminar facet screws.As shown in FIG. 19, in this embodiment of use, the fixation deviceextends through the spinous process and facet of a first vertebra andinto the facet of a second, typically inferior, vertebra. As with theprevious embodiment, this procedure is typically (but not necessarily)preformed with bilateral symmetry. In one embodiment, the body 28 offixation devices 12A, 12B has a length of approximately 50 mm-90 mm andthe diameter of the body is approximately 4 mm to 5.5 mm.

FIG. 20 illustrates another modified arrangement for spinal fixation inwhich the fixation device 12A″, 12B″ is used as a facet-pedical screw(e.g., as used in the Boucher technique). In such an embodiment, thefixation device extends through the facet of a first vertebra and intothe pedicle a second, typically inferior, vertebra. As with the previousembodiment, this procedure is typically (but not necessarily) preformedwith bilateral symmetry. In such an embodiment, the fixation device 12A,12B the body 28 is approximately 20-40 millimeters in length and 3.0-5.5millimeters in diameter.

In the embodiments of FIGS. 18, 19 and 20, the flange of the proximalanchor is typically supported directly against the outer surface of avertebra. Because the outer surface is typically non-planar and/or theinsertion angle of the fixation device is not perpendicular to the outersurface, an angularly fixed flange may contact only a portion of theouter surface. That is, the contact surface of the flange may not sitflush on the outer surface of the vertebra. This may cause the vertebrato crack due to high stress concentrations. This can result in poorfusion rates.

As such, in these applications, the angularly adjustable flanges of theembodiments described with reference to FIGS. 7-15 are particularlyadvantageous because the flange can rotate with respect to the body andthereby the bone contacting surface may be positioned more closely tothe outer surface of the vertebra. This results in more bone contactingsurface being utilized and the stress supported by the fixation deviceis spread out over a larger area of the vertebra. These angularlyadjustable flanges may also be used with the spinal cages and rods. Insuch embodiments, the angle of the body fixation device may be not beperpendicular to the contact surface of the fixation rod or plate. Insuch situations, the angularly adjustable flange allows the flange torotate and sit flush against the fixation rod and plate. In theembodiment described with respect to FIGS. 7 and 9, openings may beprovided in the flange so that the flange may be coupled to the fixationrod or plate by for example screws or bolts.

In the above embodiments, it may be advantageous to drill a counter boreinto the first vertebra for receiving a portion of the proximal anchor.In such embodiments, the counter bore will typically have a diameterthat is slightly larger than the outer diameter of the proximal anchorso that the proximal anchor may sit at least partially below the outersurface of the vertebra.

In certain regions of the spine, the dimension transverse to a facetjoint and through the adjacent facets is relatively small. In thesecircumstances, the fixation may desirably include a through bore,opening through the distal cortex of the distal facet. The fixationdevice described above may be utilized either in a blind holeapplication, which the distal anchor is buried within the bone, or athrough bore application is which the distal helix extends into andpotentially through the distal cortex. However, a through bore fixationdevice such as the fixation device 500 illustrated in FIGS. 21-23 mayalso be used.

As shown in FIGS. 21-23, the through bore bone fixation device 500includes a body 28 extending between a proximal end 30 and a distal end32. The distal end 32 includes a distal anchor 34 which will bedescribed in more detail below. The proximal end 30 may include breakpoints 31. In other embodiments, the proximal end 30 may not includebreak points 31 or may be used with a pull pin 38 as described abovewith reference to FIG. 4.

Retention structures 58 are spaced axially along the body 28 between aproximal limit 62 and a distal limit 64. As with the previousembodiments, the retention structures 58 may be configured to interactwith a proximal anchor to permit one way ratchet like movement and/orscrew-type movement. The body 28 may be used with any of the proximalanchors described above including the angularly adjustable flanges andproximal anchors described above with respect to FIGS. 7-15.

The distal anchor 34 comprises a plurality of friction enhancing orinterference fit structures such as ramped extensions or barbs 502, forengaging the distal cortical bone or other surface or interiorcancellous bone.

Although the illustrated embodiment includes four barbs 502, oriented at90° with respect to each other, anywhere from one to about twelve ormore barbs 502 may be utilized as will be apparent to those of skill inthe art in view of the disclosure herein. The barbs 502 may be radiallysymmetrically distributed about the longitudinal axis of the body 28.Each barb 502 is provided with a transverse engagement surface 504, forcontacting the distal surface of the cortical bone or other structure orsurface against which the barb 502 is to anchor. Transverse engagementsurfaces 504 may lie on a plane which is transverse to the longitudinalaxis of the body 28, or may be inclined with respect to the longitudinalaxis of the body 28.

In order to facilitate the radially inward compression of the barbs 502during the implantation process, followed by radially outward movementof the barbs 502 to engage the distal bone surface, each barb 502 in theillustrated embodiment is carried by a flexible or hinged lever arm 506.Lever arms 506 may be formed by creating a plurality of axial slots 508in the sidewall of the body. The axial slots 508 cooperate with acentral lumen 510 to isolate each barb 502 on a unique lever arm 506.The axial length of the axial slots 508 may be varied, depending uponthe desired length over which flexing is desirably distributed, thedesired range of lateral motion, and may vary depending upon the desiredconstruction material.

The circumferential width of the slots 508 at the distal end 30 isselected to cooperate with the dimensions of the barbs 502 to permitradial inward deflection of each of the barbs 502 so that the body 26may be press fit through a predrilled hole having an inside diameterapproximately equal to the outside diameter of the pin 28 just proximalto the transverse engagement surfaces 502. For this purpose, each of theslots 508 tapers in circumferential direction width from a relativelylarger dimension at the distal end 30 to a relatively smaller dimensionat the proximal limit of the axial slot 508.

The fixation device 500 may be used with a locking guide wire 520. Theguide wire has a distal end 522 and a proximal end 524. The illustratedguide wire 520 comprises a locking portion 526 that is located at thedistal end 522 of the guide wire 520 and an elongated portion 528 thatpreferably extends from the distal portion 522 to the proximal end 524of the guide wire 520. The diameter D1 of the elongated portion 528 isgenerally smaller than the diameter D2 of the locking portion 526. Theguide wire 502 can be made from stainless steel, titanium, or any othersuitable material.

The locking portion 526 on guidewire 502 can take any of a variety offorms, and accomplish the intended function as will be apparent to thoseof skill in the art in view of the disclosure herein. For example, agenerally cylindrical locking structure, as illustrated, may be used.Alternatively, any of a variety of other configurations in which thecross section is greater than the cross section of the proximal portion528 may be used. Conical, spherical, or other shapes may be utilized,depending upon the degree of compression desired and the manner in whichthe locking portion 156 is designed to interfit with the distal end 30of the pin.

The guide wire 502 is configured such that its proximal end can bethreaded through the lumen 510 of the pin 26. With reference to FIG. 22,the lumen 510 preferably comprises a first portion 530 and a secondportion 532. The first portion 530 is generally located at the distalend 30 within the region of the lever arms of the pin 26. The secondportion 532 preferably extends from the first portion 530 to theproximal end 28 of the pin 28. The inside diameter of the first portion530 is generally larger than the diameter of the second portion 532. Assuch, the junction between the first portion 530 and the second portion532 forms a transverse annular engagement surface 534, which liestransverse to the longitudinal axis of the body 28.

As mentioned above, the guide wire 520 is configured such that itsproximal end can be threaded through the lumen 510 of the body 38. Assuch, the diameter D1 of the elongated portion 528 is less than thediameter of the second portion 530 of the lumen 11. In contrast, thediameter D2 of locking portion 526 preferably is slightly smaller thanequal to or larger than the diameter of the first portion 530 and largerthan the diameter of the second portion 532. This arrangement allows thelocking portion 536 to be retracted proximally into the first portion530 but prevents the locking portion 536 from passing proximally throughthe body 28.

In addition, any of a variety of friction enhancing surfaces or surfacestructures may be provided, to resist distal migration of the lockingguidewire 502, post deployment. For example, any of a variety ofradially inwardly or radially outwardly directed surface structures maybe provided along the length of the locking guidewire 520, to cooperatewith a corresponding surface structure on the inside surface of thelumen 510, to removably retain the locking guidewire 520 therein. In theembodiment, a cylindrical groove is provided on the inside surface ofthe lumen 510 to cooperate with annular ridge 540 on the outsidediameter of the locking portion 526. The complementary surfacestructures may be toleranced such that the locking guidewire or guidepin may be proximally retracted into the lumen 520 to engage the lockingstructure, but the locking structure provides a sufficient resistance todistal migration of the locking guidewire 502 such that it is unlikelyor impossible to become disengaged under normal use. To further resistproximal migration of the 502, the illustrated locking portion 526 alsoincludes an radially outwardly directed flange 542.

In use, after the clinician assesses the bone, selects a bone drill anddrills a through hole, the distal end of the guide wire 520 and thedistal end 30 of the body 28 are advanced through the through hole untilthe distal portion 526 and the barbs 502 exit the distal aperture. Theproximal anchor may be positioned on the bone fixation device 500 priorto positioning of the pin body 28 in the through hole, or followingplacement of the pin body 28 within through hole.

The guide wire 520 is preferably thereafter retracted until the distalportion 526 enters, at least partially, the first portion 530 of the pin26. The proximal anchor 36 can then be rotated or otherwise distallyadvanced with respect to the body 28 so as to seat the distal anchor 34snugly against the distal component of the bone or a fixation plate orrod. As such, at least a part of the distal portion 526 of the guidewire 520 becomes locked within the body 28. This prevents the barbs 502and lever arms 506 from being compressed radially inward and ensuresthat the barbs 502 remain seated snugly against the distal component ofthe bone.

Following appropriate tensioning of the proximal anchor, the proximalend of the body 32 and the proximal end of the guide wire 520 arepreferably cut off or otherwise removed.

Additional details of the illustrated fixation device including modifiedembodiments are disclosed in U.S. application Ser. No. 09/815,263 filedMar. 22, 2001 entitled Bone Fixation System, the entirety of which isincorporated by reference herein, may also be utilized.

In use, the fixation pin of FIGS. 21-23 may be used in any through boreapplications such as between adjacent facets or other structuralcomponents of the spine. This includes both the fixation of adjacentbone fragments with or without the attachment of additional hardwaresuch as plates and rods, as has been discussed elsewhere herein. Thefixation pin 500 may also be used to engage the distal surface of theproximal cortex, to achieve fixation in the spine.

The fixation devices described above may be made from eitherconventional bioabsorbable materials or conventional non-absorbablematerials, combinations thereof and equivalents thereof. In addition,natural materials such as allografts may be used. Examples of absorbablematerials include homopolymers and copolymers of lactide, glycolide,trimethylene carbonate, caprolactone, and p-dioxanone and blendsthereof. The following two blends may be useful: 1) the blend ofpoly(p-dioxanone) and a lactide/glycolide copolymer, as disclosed inU.S. Pat. No. 4,646,741 which is incorporated by reference and (2) theglycolide-rich blend of two or more polymers, one polymer being a highlactide content polymer, and the other being a high glycolide contentdisclosed in U.S. Pat. No. 4,889,119 which is incorporated by reference.Additional bioabsorbable materials are disclosed in copendingapplication Ser. No. 09/558,057 filed Apr. 26, 2000, the disclosure ofwhich is incorporated in its entirety herein by reference.

The fixation devices may also be made from conventional non-absorbable,biocompatible materials including stainless steel, titanium, alloysthereof, polymers, composites and the like and equivalents thereof. Inone embodiment, the distal anchor comprises a metal helix, while thebody and the proximal anchor comprise a bioabsorbable material.Alternatively, the distal anchor comprises a bioabsorbable material, andthe body and proximal anchor comprise either a bioabsorbable material ora non-absorbable material. As a further alternative, each of the distalanchor and the body comprise a non-absorbable material, connected by anabsorbable link. This may be accomplished by providing a concentric fitbetween the distal anchor and the body, with a transverse absorbable pinextending therethrough. This embodiment will enable removal of the bodyfollowing dissipation of the pin, while leaving the distal anchor withinthe bone.

The components of the invention (or a bioabsorbable polymeric coatinglayer on part or all of the anchor surface), may contain one or morebioactive substances, such as antibiotics, chemotherapeutic substances,angiogenic growth factors, substances for accelerating the healing ofthe wound, growth hormones, antithrombogenic agents, bone growthaccelerators or agents, and the like. Such bioactive implants may bedesirable because they contribute to the healing of the injury inaddition to providing mechanical support.

In addition, the components may be provided with any of a variety ofstructural modifications to accomplish various objectives, such asosteoincorporation, or more rapid or uniform absorption into the body.For example, osteoincorporation may be enhanced by providing amicropitted or otherwise textured surface on the components.Alternatively, capillary pathways may be provided throughout the bodyand collar, such as by manufacturing the anchor and body from an opencell foam material, which produces tortuous pathways through the device.This construction increases the surface area of the device which isexposed to body fluids, thereby generally increasing the absorptionrate. Capillary pathways may alternatively be provided by laser drillingor other technique, which will be understood by those of skill in theart in view of the disclosure herein. In general, the extent to whichthe anchor can be permeated by capillary pathways or open cell foampassageways may be determined by balancing the desired structuralintegrity of the device with the desired reabsorption time, taking intoaccount the particular strength and absorption characteristics of thedesired polymer.

One open cell bioabsorbable material is described in U.S. Pat. No.6,005,161 as a poly(hydroxy) acid in the form of an interconnecting,open-cell meshwork which duplicates the architecture of human cancellousbone from the iliac crest and possesses physical property (strength)values in excess of those demonstrated by human (mammalian) iliac crestcancellous bone. The gross structure is said to maintain physicalproperty values at least equal to those of human, iliac crest,cancellous bone for a minimum of 90 days following implantation. Thedisclosure of U.S. Pat. No. 6,005,161 is incorporated by reference inits entirety herein.

In the embodiments described above, it should be appreciated that thedistal anchor may be configured to be used with a pre-drilled holeand/or self tapping.

The components of the present invention may be sterilized by any of thewell known sterilization techniques, depending on the type of material.Suitable sterilization techniques include heat sterilization, radiationsterilization, such as cobalt 60 irradiation or electron beams, ethyleneoxide sterilization, and the like.

The specific dimensions of any of the bone fixation devices of thepresent invention can be readily varied depending upon the intendedapplication, as will be apparent to those of skill in the art in view ofthe disclosure herein. Moreover, although the present invention has beendescribed in terms of certain preferred embodiments, other embodimentsof the invention including variations in dimensions, configuration andmaterials will be apparent to those of skill in the art in view of thedisclosure herein. In addition, all features discussed in connectionwith any one embodiment herein can be readily adapted for use in otherembodiments herein. The use of different terms or reference numerals forsimilar features in different embodiments does not imply differencesother than those which may be expressly set forth. Accordingly, thepresent invention is intended to be described solely by reference to theappended claims, and not limited to the preferred embodiments disclosedherein.

1. A method of providing spinal fixation, comprising the steps of:providing a fixation device that comprises a body having a first portionthat forms a bone anchor and a second portion that forms a proximal end,the first and second portion of the body detachably coupled to eachother at a junction; advancing the bone anchor of the fixation devicethrough a facet of a first vertebra to position a distal tip of the boneanchor within a pedicle of a second vertebra; advancing a proximalanchor distally over retention structures on the body to reduce thedistance between the bone anchor and the proximal anchor, therebyapplying compression between the facet on the first vertebra and thesecond vertebra; and mechanically decoupling the second portion from thefirst portion after the proximal anchor is advanced distally along thefixation device.
 2. The method of claim 1, wherein the step of advancingthe bone anchor of the fixation device into a second vertebra comprisesrotating the bone anchor.
 3. The method of claim 1, comprising drillinga bore in the first vertebra having a diameter slightly larger than theoutside diameter of the proximal anchor.
 4. The method of claim 1,further comprising adjusting the angle between a longitudinal axis ofthe body and the proximal anchor with respect to a longitudinal axis ofa flange.
 5. The method of claim 1, wherein separating and removing thesecond portion from the first portion comprises rotating the secondportion with respect to the first portion.
 6. The method of claim 1,wherein the second portion of the body comprises part of a device usedto advance the bone anchor into the pedicle of the second vertebra. 7.The method of claim 1, wherein the first vertebra is the L-5 vertebraand the second vertebra comprises the S-1 portion of the sacrum.
 8. Themethod of claim 1, wherein the first and second vertebra are in acervical region of a spine.
 9. The method of claim 1, further comprisingadvancing the proximal anchor distally along the fixation device beforethe body is advanced through the facet of the first vertebra.
 10. Themethod of claim 1, comprising advancing the proximal anchor distallyalong the fixation device after the bone anchor is advanced into thepedicle of the second vertebra.
 11. The method of claim 1, wherein stepof advancing the proximal anchor over the retention structures comprisesadvancing the proximal anchor over at least 10% of the overall length ofthe fixation device.
 12. The method of claim 1, wherein step ofadvancing the proximal anchor over the retention structures comprisesadvancing the proximal anchor over at least 20% of the overall length ofthe fixation device.
 13. The method of claim 1, wherein step ofadvancing the proximal anchor over the retention structures comprisesadvancing the proximal anchor over at least 50% of the overall length ofthe fixation device.
 14. The method of claim 1, wherein the step ofadvancing the proximal anchor over the retention structures comprisesadvancing the proximal anchor over a series of ridges.
 15. A method oftreating the spine, comprising the steps of: providing a fixation devicethat comprises a body having a distal anchor and a proximal anchor;advancing the distal anchor of the fixation device through a facet of afirst vertebra and into a pedicle of a second vertebra; rotating thefixation device to engage the distal anchor with the pedicle; and movingthe proximal anchor distally over retention structures on the body toreduce the distance between the distal anchor and the proximal anchor,such that a locking element on the proximal anchor engages at least oneretention structure on the body thereby applying compression between thefirst and second vertebra.
 16. The method of claim 15, wherein the bodycomprises distal and proximal portions that are detachably coupled toeach other at a junction.
 17. The method of claim 15, wherein the firstvertebra is the L-5 vertebra and the second vertebra comprises the S-1portion of the sacrum.
 18. The method of claim 15, wherein the first andsecond vertebra are in a cervical region of a spine.
 19. The method ofclaim 15, further comprising coupling the proximal anchor to the bodybefore the body is advanced through the facet of the first vertebra. 20.The method claim of 15, further comprising coupling the proximal anchorto the body after the distal anchor is advanced into the pedicle of thesecond vertebra.
 21. The method of claim 15, wherein step of moving theproximal anchor distally over the retention structures comprises movingthe proximal anchor over at least 10% of the overall length of thefixation device.
 22. The method of claim 15, wherein step of moving theproximal anchor over the retention structures comprises moving theproximal anchor over at least 20% of the overall length of the fixationdevice.
 23. The method of claim 15, wherein step of moving the proximalanchor over the retention structures comprises moving the proximalanchor over at least 50% of the overall length of the fixation device.24. The method of claim 15, wherein the step of moving the proximalanchor over the retention structures comprises moving a slip ring overthe retention structures.
 25. The method of claim 15, wherein the stepof moving the proximal anchor over the retention structures comprisesmoving the proximal anchor over a series of ridges.
 26. A method oftreating the spine, comprising the steps of: providing a fixation devicethat comprises a body having a distal anchor and a proximal anchor;advancing the distal anchor of the fixation device through a facet of afirst vertebra and into a pedicle of a second vertebra; rotating thefixation device to engage the distal anchor with the pedicle; moving theproximal anchor distally over retention structures on the body to reducethe distance between the distal anchor and the proximal anchor, suchthat a locking element on the proximal anchor engages at least oneretention structure on the body thereby applying compression between thefirst and second vertebra; and drilling a bore in the first vertebrahaving a diameter slightly larger than the outside diameter of theproximal anchor.
 27. The method of claim 26, further comprisingseparating and removing the proximal portion from the distal portion.28. The method of claim 27, wherein separating and removing the proximalportion from the distal portion comprises rotating the proximal portionwith respect to the distal portion.
 29. The method of claim 28, whereinthe proximal portion of the body comprises part of a device used toadvance the distal anchor into the pedicle of the second vertebra.
 30. Amethod of facet to pedicle fixation with secondary compression,comprising the steps of: providing a fixation device that comprises abody having a distal anchor and a proximal anchor; advancing the distalanchor of the fixation device through a facet of a first vertebra andinto a pedicle of a second vertebra; rotating the fixation device toengage the distal anchor with respect to the second vertebra; andaxially shortening the fixation device thereby reducing the distancebetween the distal anchor and the proximal anchor, such that a lockingelement on the proximal anchor engages at least one retention structureon the body thereby applying compression between the first and secondvertebra.
 31. The method of claim 30, wherein the body comprises distaland proximal portions of the body that are detachably coupled to eachother at a junction.
 32. The method of claim 31, further comprisingseparating and removing the proximal portion from the distal portion.33. The method of claim 32, wherein separating and removing the proximalportion from the distal portion comprises rotating the proximal portionwith respect to the distal portion.
 34. The method of claim 31, whereinthe proximal portion of the body comprises part of a device used toadvance the distal anchor into the pedicle of the second vertebra. 35.The method of claim 30, wherein the first vertebra is the L-5 vertebraand the second vertebra comprises the S-1 portion of the sacrum.
 36. Themethod of claim 30, wherein the first and second vertebra are in acervical region of a spine.
 37. The method of claim 30, furthercomprising coupling the proximal anchor to the body before the body isadvanced through the facet of the first vertebra.
 38. The method ofclaim 30, further comprising coupling the proximal anchor to the bodyafter the distal anchor is advanced into the pedicle of the secondvertebra.
 39. The method of claim 30, wherein step of moving theproximal anchor distally over the retention structures comprises movingthe proximal anchor over at least 10% of the overall length of thefixation device.
 40. The method of claim 30, wherein step of moving theproximal anchor over the retention structures comprises moving theproximal anchor over at least 20% of the overall length of the fixationdevice.
 41. The method of claim 30, wherein step of moving the proximalanchor over the retention structures comprises moving the proximalanchor over at least 50% of the overall length of the fixation device.42. The method of claim 30, wherein the step of moving the proximalanchor over the retention structures comprises moving a slip ring overthe retention structures.
 43. A method of facet to pedicle fixation withsecondary compression, comprising the steps of: providing a fixationdevice that comprises a body having a distal anchor and a proximalanchor; advancing the distal anchor of the fixation device through afacet of a first vertebra and into a pedicle of a second vertebra;rotating the fixation device to engage the distal anchor with respect tothe second vertebra; axially shortening the fixation device therebyreducing the distance between the distal anchor and the proximal anchor,such that a locking element on the proximal anchor engages at least oneretention structure on the body thereby applying compression between thefirst and second vertebra; and drilling a bore in the first vertebrahaving a diameter slightly larger than the outside diameter of theproximal anchor.